Unitary, double-ended connector for optical fibres

ABSTRACT

An optical fibre-connecting device includes a passageway which is funnel-shaped at both ends thereof and with which an optical fibre is intended to be inserted from either end into the passageway, so that the fibres will meet one another therein. The connecting device (1) includes a first silicon part (7) having a flat surface in which one or more grooves (8) of V-shaped cross-section have been etched. Additionally the connecting device (1) includes a second part (9) which is made of transparent glass and which has a flat side that is intended to abut the grooved surface of the first part (7) so as to form a channel of triangular cross-section, wherein a circle inscribed in the channel will have a diameter which is only slightly larger than the outer diameter of an optical fibre (5, 6).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a connecting device for optical fibres.

2. Description of the Related Art

When optical fibres are used as information carrying media, it is oftennecessary to join the fibres together and also to connect the fibres tolight-transmitting and light-receiving units.

The present invention relates to a device for mutually connectingdifferent kinds of fibres. Thus, the inventive connecting device can beused to join both plastic fibres and glass fibres.

A connecting device which is comprised essentially of an homogenouscylinder having a through-penetrating hole which extends along thecylinder axis is known to the art. At each end of the cylinder, there isprovided a funnel-shaped recess which is symmetrical with respect to thecylinder axis and which leads to the throughpassing hole. The connectingdevice is made from a non-transparent material.

When using this known device, the ends of respective fibres are insertedinto the funnel-shaped recess and then guided into the throughpassinghole, so as to meet one another within the device.

This known fibre-connecting device is expensive to manufacture and isencumbered with several decisive drawbacks. One drawback is that it isdifficult to achieve sufficient precision with regard to the diameter ofthe throughpassing hole. The hole diameter should be precise to atolerance of less than about 1 micrometer in order for the fibre ends tomeet one another in the manner desired, i.e. with sufficient overlap ofthe fibre cores. Another drawback is that the connecting device isintended only for one single join. A further, serious drawback is thatit is not possible to see or check the positions of the fibre ends inthe fibre-connecting device.

These drawbacks are eliminated by means of the present invention, whichprovides a fibre-connecting device of high precision and of relativelyinexpensive manufacture.

SUMMARY OF THE INVENTION

Accordingly, the present invention relates to an opticalfibre-connecting device which includes a passageway which isfunnel-shaped at both ends thereof and with which an optical fibre isintended to be inserted from either end into the passageway, so that theoptical fibres will meet therein. The connecting device includes a firstsilicon part which has etched in one flat surface thereof one or moregrooves of V-shaped cross-section. The connecting device includes asecond part which is made of transparent glass and which has a flat sidewhich is intended to lie against the grooved surface of said first part,so as to form a channel of triangular cross-section, where a circleinscribed in said channel will have a diameter which only slightlyexceeds the outer diameter of an optical fibre.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference to theexemplifying embodiments thereof and also with reference to theaccompanying drawings, in which

FIG. 1 is a longitudinal sectional view of an inventive connectingdevice;

FIG. 2 is a perspective view of part of a connecting device;

FIG. 3 illustrates part of a connecting device according to FIG. 1 seenfrom above;

FIG. 4 is a side view of part of a connecting device and an adapter;

FIG. 5 illustrates the connecting device and adapter of FIG. 4 fromabove;

FIG. 6 illustrates an embodiment of the connecting device in which thedevice functions as a coupling unit;

FIG. 7 illustrates schematically a complete coupling unit which includesthe connecting device; and

FIG. 8 illustrates one end of a so-called ribbon.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates an optical fibre-connecting device 1 which includes apassageway 2 which is funnel-shaped at both ends 3, 4 thereof, where anoptical fibre 5, 6 is intended to be inserted into the passageway fromeach end, as shown by the arrows, so that the optical fibres will meetin the passageway.

According to the invention, the connecting device includes a firstsilicon part 7 having a flat surface in which one or more grooves 8 ofV-shaped cross-section have been etched. The connecting device alsoincludes a second part 9, which is made of transparent glass material.The second part 9 has a flat side 10 which is intended to lie againstthe grooved surface 11 of the first part 7, such as to form a channel oftriangular cross-section. A circle inscribed in this channel will have adiameter which only slightly exceeds the outer diameter of the opticalfibre.

Each of the V-shaped grooves 8 at opposing ends 3, 4 of the connectingdevice has a deeper and broader section 12, such as to provide afunnel-shaped section at each said end 3, 4, as shown in FIGS. 1 and 3.FIG. 3 illustrates in dark, broad lines, the flat ridges 13 that extendbetween the V-shaped grooves 8.

According to one greatly preferred embodiment of the invention, theaforesaid first part of the connecting device is comprised ofcrystalline silicon having the crystal direction [1 0 0]. In practice,the first part of the connecting device is conveniently produced from acrystalline silicon plate having the crystal direction [1 0 0], athickness of 525 micrometers and a diameter of 4 inches, i.e. a standardsilicon sheet.

This choice of material will enable the grooves 8 to be wet-etched withthe aid of a conventional photolithographic mask. The grooves are etchedby applying a mask whose extension corresponds to the ridges 13. Ananisotropic wet-etching process is then carried out, for instance withpotassium hydroxide (KOH). The plate, or sheet, is etched to obtain thecrystal plane [1 1 1]. The etching process is halted where these planesmeet, V-shaped grooves having flat sides which define an angle of 54.7°with the upper surface of the plate being formed. The etching process iscontinued outside the mask, so as to form the funnel-shaped sections 12.

The aforedescribed method results in very high precision with regard tothe dimensions and positions of the grooves 8.

According to another preferred embodiment, the second part 9 of theconnecting device is comprised of silicate glass, preferably a boronsilicate glass. Boron glass is preferred because it has generally thesame coefficient of linear expansion as silicon. The glass willpreferably have a thickness of about 0.5 millimeter.

After completion of the etching process, the flat undersurface of thesecond part 9 of the connecting device is placed on the first part 7.The parts 7, 9 are then joined together, preferably with the aid of ananodic bonding process. Bonding can be achieved by applying a voltage,e.g. a voltage of 800 Volts, vertically in FIG. 1, at a temperature ofabout 450° C.

The advantage of anodic bonding is that no glue need be used. When glueis used, there is a risk that glue may enter the grooves. Furthermore,it may be difficult to determine the thickness of glue joints, meaningthat the cross-section of the grooves will not be well defined.

The grooves 8 thus have a cross-section in the shape of an isoscelestriangle, into which the fibres are inserted.

Naturally, the precision to which the fibres are positioned in thegroove will depend on how much smaller the outer diameter of the fibresis than the diameter of the circle inscribed in the groove. Ideally, theouter diameter of the fibre will coincide with the diameter of theinscribed circle. However, a certain degree of clearance must be foundbetween fibre and groove, in order for it to be possible to insert thefibre into the groove.

A glass fibre which includes an optically conductive core will typicallyhave an outer diameter of 125 micrometers. The optically conductive corehas typically a diameter of 5 micrometers. The intention is that twofibre ends shall meet in the connecting device, as illustrated in FIG.1, such that the cores will lie opposite one another. The cores shouldnot be displaced radially in relation to one another by more than onemicrometer.

According to one preferred embodiment, when the connecting device isintended to join together optical fibres that include an opticallyconductive core, the connecting device is so constructed that the outerdiameter of the inscribed circle will exceed the outer diameter of thefibre by at most 25% of the core diameter, preferably by at most 10% ofsaid core diameter.

When effecting a join, a so-called index matching liquid 14 isintroduced into the passageway, by applying the liquid to one or bothends of the fibres prior to inserting the fibres into the connectingdevice. The index-matching liquid is a liquid which has the samerefractive index as the core material. The index-matching liquid may bean oil, for instance. The skilled person is able to select anappropriate liquid according to the fibre material concerned. Thisliquid assists in maintaining low transition losses at the fibre joinand also has a certain lubricating effect which facilitates insertion ofthe fibres into the connecting device.

Subsequent to having placed the fibres in the connecting device in theintended manner, glue 15 is applied to the ends of said device so as tofixate the fibres.

In the illustrated embodiment, each connecting device includes a numberof grooves 8. It will be understood, however, that the connecting devicecan be constructed to include solely one single groove. When the deviceincludes several grooves, a suitable groove spacing is 250 micrometers.

The inventive optical fibre-connecting device has three decisiveadvantages. Firstly, the device is extremely precise with regard to thedimensions and positions of the grooves. Secondly, and very importantly,the fibre ends can be seen through the glass. This can be achievedin-practice with the naked eye, without needing to use opticalauxiliaries. This enables the positions of the fibres to be readilychecked. Thirdly, the inventive optical fibre-connecting device can bemanufactured cheaply. For instance, the silicon part of about 100connecting devices can be produced simultaneously from a single siliconplate 4 inches in thickness.

The present invention therefore provides a significant advantage incomparison with known techniques.

According to one preferred embodiment, insertion of the fibres isfacilitated by means of an adapter 16, shown in FIGS. 4 and 5, which isintended to lie against the ends 3, 4 of the connecting device 1 wherethe triangular channels open out, at least when inserting the fibresinto said device. The adapter 16 includes a V-shaped groove 17 for eachof the triangular channels 8 of the connecting device 1. The V-shapedadapter groove 17 widens and deepens in an outward direction away fromthe connecting device.

The adapter 16 may be made of a plastic material. The adapter 16 mayalso be provided with a recess 18 which connects with the connectingdevice 1, so as to enable the connecting device to be positioned morereadily in relation to the adapter 16. Because the adapter groove widensin an outward direction away from the connecting device, a fibre 6 canbe placed easily in a groove in the adapter. As the fibre is then pushedtowards the connecting device the fibre will be guided into the actualconnecting device by means of the adapter 16.

According to one preferred embodiment of the invention, the groove 17 inthe adapter 16 is curved in the symmetry plane extending through thebottoms of respective V-shaped grooves, i.e. the adapter curvesoutwardly from the connecting device, as illustrated in FIG. 4.Reference numeral 19 identifies the bottom of a groove 17, which isshown to extend in a curved path.

The main reason, and an important reason, for this construction is thatbecause the fibre is moved in a curved path the leading end of the fibrewill be pressed against the bottom of the groove 8 in the connectingdevice. This means that the fibre will be positioned against the groovebottom when a gap is found between the outer surface of the fibre andthe walls of the triangular groove. When the fibre introduced into theconnecting device from the other end thereof is also inserted with theaid of the adapter, this fibre will also be positioned against thebottom of the groove in the connecting device. Thus, the two fibres willbe well-positioned in relation to one another, even when the outerdiameters of the fibres are smaller than the diameter of the inscribedcircle to a greater extent than the diameter of the fibre cores. Whenusing an adapter 16 with the aforesaid curved groove, glue 15 is appliedso as to lock the fibre in position after having inserted the fibre intothe connecting device.

The present invention can be applied to join single fibres or two ormore fibres. The number of grooves included in a connecting device willtherefore depend on the actual application of the device.

So-called fibre ribbons can also be connected. A so-called fibre ribbon30 is a ribbon which contains a number of mutually parallel fibres 31.Each fibre is embedded in a cladding layer 32. The fibres are supportedby a plastic casing 33; see FIG. 8.

FIG. 8 illustrates one end of a ribbon and shows part of the plasticcasing peeled away and part of the cladding layers stripped-off.

When the distance between the grooves 8 is 250 micrometers, whichcorresponds to the distance between the fibres in the ribbon 30, allfibres can be joined at one and the same time, by introducing the end ofthe ribbon to a connecting device which has at least as many grooves asthere are fibres in the ribbon.

In the aforegoing, the connecting device has been described solely withreference to its use in achieving a permanent fibre connection.According to one preferred embodiment, however, the connecting devicemay have the form of a coupling unit 20, 21, see FIGS. 6 and 7, withwhich one or more fibres 22 is/are inserted into the connecting device 1from one side 23 thereof and fastened in relation to said device, andwith which the other side 24 of the connecting device is intended toreceive fibres 25 for insertion of said fibres into said device.

That side of the connecting device in which the fibres are permanentlyinserted may be moulded in a plastic holder 30; see FIG. 6.

The connecting device 1 may be embraced by a female part 26 of aconventional coupling unit, for instance a coupling unit of the kindused to connect together electrical conductors, see FIG. 7, said femalepart being provided with hooks 27 which coact with hooks 28 on a malepart 29 of the coupling unit. In this case, the male part 29 carriesfibres 25 which are spaced apart at a distance corresponding to thespacing of the grooves in the connecting device.

The coupling unit is preferably configured so that the male and femaleparts will include conventional guides (not shown) which function tobring the male part to a correct position in relation to the female partprior to said parts being pressed together and thus prior to the fibres25 being led into the connecting device 1. According to one embodiment,the coupling unit is of a kind in which the female and male parts can bepushed together and mutually separated.

When concerning coupling units of this nature, it is advantageous toproceed from the aforesaid ribbon 30 which is provided with a male part29.

It will be evident from the aforegoing that the present inventionovercomes the drawbacks mentioned in the introduction and provides ahighly advantageous connecting device.

The invention has been described in the aforegoing with reference todifferent exemplifying embodiments thereof. It will be understood,however, that the present invention can be varied with regard todimensions and structural details.

The present invention shall not therefore be considered limited to theaforedescribed embodiments thereof, since modifications and variationscan be made within the scope of the following claims.

We claim:
 1. An optical fibre-connecting device for connecting a pair of optical fibres in coaxial relationship, said device comprising: a body member having a passageway which is funnel-shaped at both ends thereof and into which passageway an optical fibre is intended to be inserted from either end thereof, so that a pair of fibres inserted at respective opposite ends of the passageway will meet one another in the passageway, the body member including a first silicon part having a flat surface in which a groove of V-shaped cross-section has been etched and wherein the body member includes a second part covering said groove so that a channel with a triangular cross section is formed, wherein during said etching the V-shaped groove has been etched to a deeper and wider section at opposite ends of the body member so as to form a funnel-shaped section at each passageway end, wherein said second part is made from transparent glass material which has a flat side lying against the grooved surface of the first part to enable visual determination of fibre position within the passageway, and wherein the grooved surface of the first part and the flat side of the second part of the body member are joined together by means of an anodic bond whereby said channel of triangular cross-section is formed, wherein a circle inscribed in said channel will have a diameter which only slightly exceeds the outer diameter of the optical fibre.
 2. A device according to claim 1, wherein when the connecting device is intended to mutually connect optical fibres that include a light conductive core, the outer diameter of said inscribed circle will exceed the outer diameter of the fibre by at most 25% of the core diameter.
 3. A device according to claim 1, wherein the device includes at least two parallel, fibre-receiving grooves which together with said funnel-shaped section are made by etching.
 4. A device according to claim 1, wherein the first part is made from crystalline silicon having the crystal direction; and wherein the second part is made from silicate glass.
 5. A device according to claim 1, wherein the connecting device includes a fibre guide which is adapted to lie against an end of the connecting device adjacent a triangular channel when inserting a fibre into said connecting device; and wherein the fibre guide includes a V-shaped guide groove for each triangular channel of the connecting device, said V-shaped guide grooves widening and deepening in an outward direction away from the connecting device.
 6. A device according to claim 5, wherein the guide grooves of said fibre guide curve in a symmetry plane that extends through bottom portions of respective V-shaped guide grooves.
 7. A device according to claim 1, wherein the connecting device forms a coupling unit in which fibres are inserted into the connecting device from one side thereof and fastened in relation to the connecting device, and wherein an opposite side of the connecting device is adapted to receive additional fibres.
 8. A device according to claim 1, wherein said first part is a silicon plate having a thickness of 525 micro-meters; and wherein said second part is a glass plate having a thickness of about 0.5 millimeter.
 9. A device according to claim 3, wherein the fibre-receiving grooves have a mutual spacing of 250 micrometers.
 10. A device according to claim 1, wherein when the connecting device is intended to mutually connect optical fibres that include a light conductive core, the outer diameter of said inscribed circle exceeds the outer diameter of the fibre by at most 10% of the core diameter.
 11. A device according to claim 1, wherein the first part is made from crystalline silicon having the crystal direction; and wherein the second part is made from a boron silicate glass. 